U.S. Pat. No. 4,397,937 of Clecak et al shows sensitizers which are esters of 1-oxo-2-diazonaphthalene sulfonic acid and of certain diols including tricyclodecane derivatives. This patent is concerned exclusively with esters of diols and can be said to direct attention away from the present invention, which is concerned only with esters of monohydroxy alcohols. The compounds of the prior art patent, when used at 365 nm, have much higher optical density than the compounds of the present invention at loadings required to achieve high contrast performance. These materials are superior for use at shorter wavelengths (i.e. 313 nm).
European patent application No. 0147596 of Economy et al shows esters of 1-oxo-2-diazonaphthalene sulfonic acid and certain diols. It discloses no monoesters.
U.S. Pat. No. 3,640,992 of Sus et al issued in 1972. It discloses a single compound, namely the p-cumylphenol ester of 1,2-napthaquinone diazide(2)4-sulfonic acid. Prior to the present invention, this compound of Sus has, for 15 years, been the most soluble diazoquinone monoester known. The monoesters of the present invention are more soluble than the Sus compound, and have the added advantage of better absorbance and improved bleaching.